BREATHING MODULATION OF CARDIOPULMONARY COUPLING – A POTENTIAL WAY OUT OF AUTONOMIC DECONDITIONING AFTER PROLONGED MICROGRAVITY EXPOSURE

Microgravity causes a specific consequence on cardiovascular system – an orthostatic intolerance experienced by astronauts after long space flights. The major reason for this phenomenon is deconditioning of the cardiovascular autonomic regulation due to microgravity environment. Sympathetic withdrawal is the consequence of cephalad shift of blood and body fluids which is considered as a primary cause of several neurophysiologic disturbances during the space flight and postflight recovery (postural hypotension, sleep disturbances, low stress coping abilities). Cardiopulmonary coupling is the issue that potentially offers the possibility of the autonomic conditioning before and during the spaceflight. In humans, as opposed to cardiac rhythm, breathing can undergo volitional control. Paced 0.1 Hz breathing rhythm is characteristic, resonant frequency of many autonomic and cortical circuits, which amplifies heart rate modulation on one side, and recruits central cortical and subcortical circuits resulting in increased sleep propensity and relaxed attentive consciousness. We applied a battery of coefficients estimating the change of self-similarity and irregularity of heart rate and respiratory rate in four different states: supination, standing, supination with 0.1 Hz breathing and standing with 0.1 Hz breathing (Matić et al. 2020). Additionally, we analysed the posture and breathing regime dependence of quotient of pulse per respiration (Qpr), the number of heartbeats in each respiratory cycle. Chosen parameters are of importance for evaluation of cardiopulmonary adaptability and plasticity. Our results (Matić et al. 2020) and state dependent Qpr relation vs. breathing rate support the evidence that cardiorespiratory coupling and cardiorespiratory variability are posture and breathing regime dependent, with the state of combined standing with 0.1 Hz breathing identified as the state with maximal conditioning effect on heart rate, respiratory rate, and cardiorespiratory coupling. We propose this manoeuvre as the autonomic conditioning strategy for the crew before long space flights.